1. Field of the Invention
This invention relates to zoom lenses suited to photographic cameras or video cameras and, more particularly, to zoom lenses having three lens units with the lens unit of negative power preceding, these three lens units being made to move when varying the magnification, thus shortening the total length of the lens, minimizing the bulk and size and maintaining good optical performance.
2. Description of the Related Art
There have been previous proposals for a zoom lens comprising, from front to rear, a first lens unit of negative power, a second lens unit of positive power and a third lens unit of negative power, all these three lens units being made to move when varying the focal length, in, for example, Japanese Laid-Open Patent Application No. Sho 64-72114.
This type of zoom lens is amenable to a relatively wide image angle at the wide-angle end and, therefore, has found its use in many wide-angle photographic systems.
In the same document, conditions are set forth for moving the first, second and third lens units, and the construction and arrangement of the three lens units are specified for good stability of aberration correction against zooming, thereby achieving a zoom lens of high optical performance in a zoom ratio of 2-3. The zoom lens comprises 8-9 lens elements as a whole, and is relatively compact, so it is suited particularly to the lens-shutter camera.
The above-described proposal of the Japanese Laid-Open Patent application No. Sho 64-72114 provides for shortening the optical total length of a zoom lens (or the distance from the front vertex to the focal plane) by using two or more lens elements in constructing each of the lens groups. This affords to strengthen the refractive power of every lens unit in such a manner that, for example, chromatic aberrations are corrected in each individual lens unit.